Variable pitch rotary blading

ABSTRACT

In a variable pitch fan gas turbine engine an actuator for changing the pitch of the blades is connected to each blade through two driving connections in parallel. The first driving connection is a relatively flexible shaft, and the second is a relatively stiff hollow shaft which surrounds the first shaft and is connected to it by means of splines. This arrangement allows for bending of the first-mentioned shaft and tilting of the hollow shaft to provide for relative movements between the actuator and the blades.

United States Patent 1191 McMurtry Dec. 25, 1973 [54] VARIABLE PITCHROTARY BLADING 2,533,358 12/1950 Cushman 416/89 3,663,119 5/1972Brooking et a1.

[75] 3*? 3 McMurry 3mm, 3,687,569 8/1972 Klompas 416/145 x ng an N P T[73] Assignee: Rolls-Royce, Limited, London, FOREIG A ENTS ORAPPLICATIONS England 1,370,754 7/1964 France 416/136 Filed! p 1972Primary Examiner-Everette A. Powell, Jr. [21] AppL 248,410Attorney-Richard K. Stevens et al.

[30] Foreign Application Priority Data [57] ABSTRACT May 6 1971 GreatBritain 14 173 71 a Variable Pitch fan gas turbine engine an actuator vl for changing the pitch of the blades is connected to 1521 US. (:1.416/155 each blade through driving connections in parah 51 Int. Cl. B64011/06 The first driving Connection is a relatively flexible 5 Field ofSearch 41 145 139 155457 shaft, and the second is a relatively stiffhollow shaft 416/167, 89 136 which surrounds the first shaft and isconnected to it by means of splines. This arrangement allows for [56]References Cited bending of the first-mentioned shaft and tilting of theUNITED STATES PATENTS hollow shaft to provide for relative movementsbetween the actuator and the blades. 2,460,559 2/1949 Wildhaber 416/892,514,477 7/1950 Cushman 416/89 4 Claims, 2 Drawing FiguresPATENTEDumsms I Q 3.781.131

' SHEEIIUFZ FIG. 1.

PATENTED UEEZ 5 I975 saw 2 0F 2 FIG. 2

VARIABLE PITCH ROTARY BLADING The present invention relates to pitchchanging mechanism for variable pitch rotary blading.

According to the present invention, there is provided a rotor, aplurality of blades mounted on said rotor for rotation about theirlongitudinal axes to vary their pitch and a pitch changing mechanism foreffecting said rotation, said pitch changing mechanism comprising anactuator, a plurality of driving members each defining a firstdrivingconnection between the actuator and one of the blades, and a pluralityof driving elements each defining a second driving connection betweenthe actuator and a respective one of the blades in parallel with thefirst connection, said driving elements each being adapted to allowdeflection of the respective driving member whilst being capable oftransmitting the torque required to vary the pitch of the blade inoperation.

In a preferred form of the invention the driving mem-,

bers are relatively flexible, and the driving elements are relativelystiff, the driving connections formed thereby being such that thedriving members are capable of bending to a greater degree than thedriving elements and the driving elements are capable of tilting thusallowing for relative lateral movement between the blade and theactuating -means.-

Also preferably each driving member comprises a first shaft which isrelatively flexible and each driving element comprises a secondrelatively stiff hollow shaft in the form of a cylinder of a frustum ofa cone which surrounds the first shaft.

The first driving connections between the actuator preferably include apair of toothed annular members driven by the actuator in oppositedirections and engaging a toothed wheel on one end of each of thedriving members, the other side of the driving members being connectedto the blades, for example, by means of screw threads.

The second driving connections between the actuator and the bladesinclude a splined connection between each driving element and thetoothed wheel on the respective driving member at one end of theelement, and a splined connection between the element and the blade atthe other end of the element. The invention will now be moreparticularly described, merely by way of example, with reference to theaccompanying drawings in which:

FIG. 1 is a diagrammatic view of a variable pitch fan engineincorporating the pitch changing mechanism the present invention.

FIG. 2 is a sectional elevation of a fan blade and rotor showing thepitch changing mechanism in greater detail. Referring now to thedrawings a gas turbine engine comprises a gas generator or core engine 1which drives a fan 2 through a gear box 3. The core engine comprises theusual compressor, combustion equipment and turbine (not shown) as arewell known in the art, all of which rotate about a main engine axis 4.

Referring to FIG. 2, the blades of the fan 2 each have a root portionwhich is mounted on a rotor 12 for rotation of its respective fan bladeabout the longitudinal axis 14 thereof. The rotor is in the form of adisc which is of open-ended channel section, having two inclined sidewalls 16 terminating in radially inner hub portions 18 and a radiallyouter end wall 20.

the outer race 22 of a bearing 24 and is splined to the outer race bymeans of splines 26. An inner race for the bearing 24 is provided by aring 28 which is screwed into one of the circular apertures in the endwall of the disc, and which also provides the outer race for a secondbearing 30. The inner race for the bearing 30 is provided-by a drivingring 32 which is splined to a pitch changng mechanism (described below)at 34, and to the outer race 22 of the bearing 24.

The outer and inner races of the bearing 24 have cylindrical extensions36 and 38 which respectively form a cam member and reaction means for amechanism designed to counter-balance the centrifugal turning moments onthe blades. This mechanism is not described in detail since it is notrelevent to the present invention.

A variable pitch mechanism extends up through the hollow interior of thedisc so that the pitch (i.e., angle of attack) of the blades can bevaried. The mechanism comprises an actuator in the form of a vane motor40 which has a semi-circular outer casing 42 carrying integrallyradially inwardly extending vanes, and a cylindrical inner casing 44carrying a second set of vanes which co-operate with the vanes on theouter casing to form chambers 46 into which hydraulic fluid underpressure can be pumped. The outer casing and the inner cylinder rotatein opposite directions under the influence of the hydraulic fluid andare connected with toothed annular members 48 and50 respectively. Atoothed bevel 52 meshes with the teeth of both annular members 48 and 50and acts via a radially extending driving member in the form of a firstshaft 54 to change the pitch of the blades.

The shaft 54 is formed integrally with a blade connecting member 56which screws into the root 10 of the blade by means of screw threads 58.A nut 60 connects the whole assembly together. Thus the toothed bevel52, the shaft 54 and the member 56 provide a first driving connectionbetween the actuator 40 and the blade.

. 6 The end wall 20 defines a series of circumferentlally spacedcircular apertures into which the circular roots 10 of the bladesextend. Each blade root is mounted in Additionally the shaft issurrounded by a driving element 62 in the form of a hollowfrusto-conical second shaft which is splined at its radially outer endsto the connecting member 56 by means of splines 64, and to the drivingring 32 by means of the splines 34. The driving element 62 is connectedat its radially inner end to the driving bevel 52 by means of splines66.

The driving elements 62 thus provide a second parallel driving path forthe torque for changing the fan blade pitch, between the bevel 52 andthe blade root 10. Because of this provision the driving shaft 54 ismade relatively flexible compared to the surrounding frusto-conicalmember 62 which is relatively stiff. The shaft 54 is capable of bendingand the frusto-conical driving element 62 is capable of tilting at thesame time, such movement being accommodated by the splines 34, 64 and66, when there is a transverse load on bevel gear 52. This arrangementallows movement of the bevel gear 52 relative to the blade root 10 in anumber of circumstances the two most important of which are:

a. There may be adiscrepancy between the mating of the toothed annularmembers 48,50 with any bevel gear 52. This is accommodated by deflectionof the bevel gear to compensate and equalise the load sharing of members48 and 50.

b. Under certain conditions of operation, for example, when the fan orpropeller blades are turned rapidly into reverse pitch during forwardmovement of the aircraft, the blades momentarily vibrate with largeamplitude. If the connection between the bevel gear 52 and the rootportion were rigid, this blade deflection could cause damage to the gearteeth of gears 48,50 and 52. This is avoided by the flexible connectionbetween root portion 10 and gear 7 which does not transmit the damagingvibratory motion.

This feature also enables the size and thus the weight of the bevel 52and the toothed annular members 48 and 50 to be minimised.

Although the embodiment described above includes a vane motor 40 as anactuator, clearly other forms of actuator may be employed, for example,a gear mechanism, and other modifications may be made without departingfrom the scope of the invention.

I claim:

1. Variable pitch rotary blading including a rotor, a plurality ofblades mounted on the rotor for rotation about their longitudinal axesto change their pitch, and a pitch changing mechanism, said mechanismcomprising an actuator, a pair of annular driving members driven by theactuator, a plurality of driven members one for each blade, meansincluding a relatively flexible shaft for connecting each of the drivenmembers with a respective blade, the annular driving members drivingonto diametrically opposite sides of all of said driven members, aplurality of relatively rigid tubes each including means for providing adriving connection between a driven member and a respective bladewhereby torque from the driven member is transmitted to the blades, saidmeans for providing a driving connection including means allowingtilting of the tubes to allow for misalignment of the driven members andthe driving members, the shafts being sufficiently flexible so that theycan bend when the tubes tilt whereby the driven members are moved tocompensate for said misalignment.

2. Variable pitch rotary blading according to claim 1 and wherein thedriving members are annular gears and the driven members are gearwheels.

3. Variable pitch rotary blading according to claim 1 and wherein thesaid means for providing a driving connection between a driven memberand a respective blade comprises a splined connection.

4. Variable pitch rotary blading according to claim 1 and wherein therelatively stiff tube surrounds the relatively flexible shaft.

1. Variable pitch rotary blading including a rotor, a plurality ofblades mounted on the rotor for rotation about their longitudinal axesto change their pitch, and a pitch changing mechanism, said mechanismcomprising an actuator, a pair of annular driving members driven by theactuator, a plurality of driven members one for each blade, meansincluding a relatively flexible shaft for connecting each of the drivenmembers with a respective blade, the annular driving members drivingonto diametrically opposite sides of all of said driven members, aplurality of relatively rigid tubes each including means for providing adriving connection between a driven member and a respective bladewhereby torque from the driven member is transmitted to the blades, saidmeans for providing a driving connection including means allowingtilting of the tubes to allow for misalignment of the driven members andthe driving members, the shafts being sufficiently flexible so that theycan bend when the tubes tilt whereby the driven members are moved tocompensate for said misalignment.
 2. Variable pitch rotary bladingaccording to claim 1 and wherein the driving members are annular gearsand the driven members are gear wheels.
 3. Variable pitch rotary bladingaccording to claim 1 and wherein the said means for providing a drivingconnection between a driven member and a respective blade comprises asplined connection.
 4. Variable pitch rotary blading according to claim1 and wherein the relatively stiff tube surrounds the relativelyflexible shaft.